HOUSTON -- Two days after his 40th birthday, Bartolo Colon pitched with youthful verve.

Colon struck out a season-high nine in seven scoreless innings, and the Oakland Athletics completed a sweep of the Houston Astros with a 6-2 win.

Oakland's Nate Freiman, who was with the Astros in spring training as a Rule 5 selection, homered, doubled and drove in three runs as the A's improved to 9-0 against the Astros this season.

Colon, who was hitting 94-95 mph on the radar throughout the game, said through an interpreter that the way he pitches, sometimes he likes to change his velocity.

Oakland manager Bob Melvin said Colon's velocity surprised him.

"Every now and then you could see him peek up there and see what the velocity was," Melvin said. "There are certain things that we can see when he knows that he's got his velocity, a little something that he does differently. Really for a guy who'll touch 93 and you'll see a 94 sprinkled in every now and then, he hovered around 94 and hit 95. So 40 years old, pretty impressive."

Colon (5-2) won his second straight start, scattering nine hits. He worked seven innings for the second straight start and for the fourth time in 10 starts this season.

Colon improved to 3-0 with a 1.89 ERA in his three starts against the Astros this season and 4-0 with a 2.53 ERA against the AL West.

Melvin thought Colon was economical with his pitches despite the hits.

"He knows how to make a pitch when he needs to and I thought his stuff actually was as good today as we've seen all year," Melvin said. "There are certain games where he knows that he has the velocity and when he can go to that, and there are certain games where he pitches a little differently. That all comes with experience and knowing yourself very well."

Freiman said he has been working in the batting cages and doing everything he can to be ready for when he is called upon to play.

"It's something that I'm excited to learn how to be a role player on this team," Freiman said. "Right now that role is to get an occasional start against left-handed starters."

Dating to 2007, Oakland has won 11 straight against Houston, tied for the third longest winning streak against one team in A's history.

"Right now if you were to look you would say, yes, they have our number," Houston manager Bo Porter said. "They've beat us nine times in nine tries and today they were just better than us."

The Astros are 14-36 in their first year in the AL, their worst 50-game start in club history.

After leaving runners on third in two of the first three innings, Oakland sent nine batter to the plate in a five-run fourth against Dallas Keuchel (1-2).

Yoenis Cespedes led off by reaching second base on an error by second baseman Jose Altuve. Josh Donaldson followed with an RBI single up the middle. After Jed Lowrie singled, Seth Smith had a run-scoring double and Freiman made it 4-0 with another double. Crisp added a two-out RBI single.

Freiman made it 6-0 with a home run to center field with one out in the in sixth.

J.D. Martinez had a one-out double off reliever Ryan Cook in the eighth and Chris Carter hit a sacrifice fly to cut it to 6-2 but that was all Houston would get.

Keuchel went six innings, giving up six runs -- four earned -- and a season-high nine hits. He struck out four.

"I think it was a mixture between me not locating and they taking advantage of it," Keuchel said. "Throw away that fourth inning and it's a 1-0 ballgame. I felt good today, but give credit to them."

Jason Castro had a career-high four hits and went 10 for 12 in the series for Houston. Castro became the first Astros player since Ty Wigginton in 2008 to have three consecutive games of at least three hits.

"I know my strengths, and part of this process is trying to match yourself up with whoever you're facing," Castro said. "It's an in-game evolution where you're always making adjustments, and I'm feeling pretty comfortable with making those adjustments on the fly right now."

NOTES: Oakland OF Josh Reddick will begin a rehab assignment Monday at Class-A Stockton, Melvin said. Reddick has been on the disabled list since May 8 with a sprained right wrist. . Lowrie started at second base Sunday after being out of the starting lineup the previous three games after being hit by a pitch on his right foot Tuesday. . Houston RHP Bud Norris will take the mound Monday against Colorado RHP Jhoulys Chacin. Norris has left each of his last two starts with back spasms. . Oakland will send RHP Dan Straily to the mound Monday to begin the Bay Area Series against the San Francisco Giants, who will counter with LHP Madison Bumgarner.